1. Technical Field
The present invention relates to an ink jet recording method, an ink set, and a recorded article.
2. Related Art
The demand for recorded articles having glittering images formed on the recording surface thereof is increasing. To form a glittering image, a foil pressing method may be performed by pressing a metal foil on a highly flat recording surface, or a metal or the like may be deposited on a plastic film having a smooth recording surface by vacuum vapor deposition. Also, a glittering pigment ink may be applied onto a recording medium, followed by pressing. These recording methods can produce recorded articles having relatively high glitter. However, in order to record glittering images in a recorded article, press molds or recording masks having the same shapes as glittering image patterns are prepared in advance, and, in addition, the process time for forming such a recorded article is increased. Accordingly, some techniques, as disclosed in JP-A-2008-174712, have been proposed which record glittering images by an ink jet method, which can perform on-demand recording at a low cost.
For an ink jet recording method achieving multicolor recording as in conventional methods, image quality as high as that produced by color photography, and increasing recording speed, many techniques have been proposed for inks improved in color developability, multicolor recording and weather fastness, and for recording media, particularly ink receiving layers, for achieving stable fixing of color materials, improving weather fastness, achieving high absorption of ink solvent (for example, JP-A-2006-263951, Japanese Patent Application No. 2005-300274, and JP-B-7-121609).
Ink receiving layers used in ink jet recording media are generally classified into two types: porous type that absorbs the ink solvent in the physical pores therein while fine silica or alumina particles having particle sizes of several tens of nanometers to several hundreds of nanometers are fixed on a base material with an organic binder; and wet type that absorbs the ink solvent in such a manner that water-soluble polymer, such as polyvinyl pyrrolidone, polyvinyl alcohol, cellulose, or urethane, fixed on a base material is wetted by the solvent. Both types contain a cationic color-fixing material that can fix coloring materials in inks to the ink receiving layer. Cationic color-fixing materials are generally classified into cation-modified polymers and cationic hydrated metal compounds. Cationic hydrated metal compounds are widely used because they are easy in handling and stable to light and environmental gases. For example, aluminum chloride-based cationic fixing materials are preferably used in practice which include chlorine as an anion component that will be released in the course of ink absorption, and aluminum hydroxide as a cation component that will be released in the course of the ink absorption, as disclosed in, for example, JP-A-2006-263951, Japanese Patent Application No. 2005-081422, and JP-A-2002-86892.
When chlorine contained as an impurity in recording media is considered, there are many recording media that contain chlorine as an impurity. For example, some recording media may contain an aluminum chloride-based fixing material, on purpose, in order to achieve high fixability. In other recording media, the ink receiving layer may contain involuntarily chlorine that has been used as an additive in the course of preparing fine alumina particles used for an ink receiving layer (for example, in the course of the process for preparing alumina disclosed in JP-A-5-24824). Also, chlorine is generally used for bleaching pulp, raw material of paper, and accordingly, recording media often contain chlorine as an impurity.
Although the chlorine content in a recording medium has a wide range from ppm order to about 1%, depending on the case where chlorine is added on purpose or on the case where it is involuntarily added, quality problems of inks, such as discoloration and degradation in light fastness, have not been caused by chlorine because chlorine does not react with coloring materials generally used in ink jet inks, that is, dyes and pigments for reproducing cyan, magenta, yellow, black and other colors.
However, it has been found that if an aqueous ink containing silver particles as a glittering material is used on chlorine-containing recording media, much superior metallic gloss can appears immediately after recording, but the image, or the gloss, of the recorded article is significantly degraded by light, relative to the cases where known color inks (cyan, magenta, yellow, block, etc.) are used. It has also been found that the gloss is noticeably degraded in colored glittering image areas (hereinafter referred to as metallic color image area).
The inventors investigated the reason why the gloss is degraded by light, and found that the following phenomena degrade the gloss of recorded articles.
When an image is formed with an aqueous ink containing silver particles, free chlorine is released and dissolved in the solvent, or water, of the ink. The free chlorine may be released from the above-described aluminum chloride-based cationic fixing agent or the impurity in the recording medium. It is generally known that chlorine and silver, irrespective of whether or not they are in ions, react directly with each other to form silver chloride. Part of the silver particles used as a glittering pigment is formed into silver chloride.
It is considered that the silver chloride formed in a recording medium is sensitive to UV light, as is clear from the fact that it is usefully used as photosensitive material in silver halide photographic films. The silver chloride formed in the recording medium is sensitized by light and forms coarse recrystallized silver on most of the surface of the recording medium, but the process of this reaction is not described in detail. The coarse recrystallized silver scatters visible light at the surface of the medium. This is the reason why light degrades the gloss of recording media.
In addition, it has been found that the photosensitivity of silver chloride, which is sensitized to produce silver by UV light having a wavelength of about 370 nm or less, is increased by contact with coloring materials contained in color inks (cyan, magenta and yellow inks), but the reason is not clear. This is the reason why gloss decrease is noticeably caused at portions where metallic color images are recorded.